(1) Field of the Invention
The present invention relates to liquid crystal display devices and, in more particular, to liquid crystal display devices of the so-called lateral electric field type.
(2) Description of the Prior Art
A liquid crystal display device categorized in the so called lateral electric field scheme is provided with respective transparent substrates opposing each other with a liquid crystal sandwiched between them, one of which has its liquid crystal-side surface with pixel regions defined thereon, in each of which a pixel electrode and an opposed electrode are disposed so that these are spaced apart from each other, the device being configured such that an electric field generatable between these respective electrodes is used to control the transmissivity of light travelling between respective electrodes.
The liquid crystal display device with the configuration above is capable of recognition of clear and crisp images even when looking at from view points at large angles with respect to its display plane, and for this reason has been known as the one that is excellent in what is called the angular viewability.
And, since the pixel electrode of each pixel region is arranged so that an image signal corresponding to the transmissivity of light to be controlled is supplied with respect to a reference signal being applied to an opposed electrode, the same signal is to be supplied via a signal line to each opposed electrode in each pixel region.
Practically, there are respective pixel regions in a display area, which are laid out in a matrix form, along with parallel opposed voltage signal lines which are formed extending in the column direction for letting respective opposed electrodes within respective pixel regions as disposed in the row direction be connected with one another; further, a common bus line is formed for connecting together these opposed voltage signal lines on one end side of each opposed voltage signal line lying outside of the display area.
More specifically, a reference signal is arranged to be supplied via the common bus line and each opposed voltage signal line to the opposed electrode in each pixel region.
Note that such arrangement has been disclosed in detail in, for example, Published Unexamined Japanese Patent Application (xe2x80x9cPUJPAxe2x80x9d) No. 6-160878.
In this case it has been pointed out that supplying the reference signal to the opposed electrode via the common bus line and each opposed voltage signal line would result in an extreme increase in distortion of signal waveform when compared to signal transmission to other electrodes.
This is because the signal line connected to the opposed electrode must be formed to be longer than those signal lines connected to the other electrodes and also because a capacitance with the liquid crystal used as its dielectric material is coupled thereto.
Due to this, typical prior art approaches have become known in which a common bus line for connecting together these opposed voltage signal lines is formed even at the remaining ends of respective opposed voltage signal lines lying outside of the display area to thereby supply the reference voltage together with the other common bus line.
In the case where respective common bus lines are formed on respective end sides of each opposed voltage signal line, a correspondingly increased space must be reserved resulting in a problem of incapability to miniaturize or shrink the so-called xe2x80x9cwindow casingxe2x80x9d frame.
It should be noted that the term xe2x80x9cwindow casingxe2x80x9d as used herein may refer to a specific portion on the display plane between its outer frame (of the display panel) and the display area, wherein shrinkage of such window casing permits enlargement of the aperture ratio of each pixel region under the assumption that the outer frame is constant while at the same time enabling down-sizing of the display panel where the aperture ratio of each pixel region is kept constant.
The present invention has been made in view of the technical background above, and its primary objective is to provide a liquid crystal display device capable of suppressing waveform distortion of more than one reference signal being supplied to opposed electrodes without suffering from an increase in window casing.
In the inventions as disclosed herein, a brief summary of a representative one of them will be set forth below.
In summary, in a liquid crystal display device which comprises respective pixel regions laid out in a matrix form in a display area on a liquid crystal-side surface of one transparent substrate of respective transparent substrates as disposed opposing each other with a liquid crystal sandwiched therebetween, and also comprises a pixel electrode and its opposed electrode disposed so that these are spaced apart from each other in each of these pixel regions, wherein the transmissivity of light passing between respective electrodes is controlled by an electric field as created between these respective electrodes, and wherein
parallel opposed voltage signal lines connecting together respective opposed electrodes within each of the pixel regions laid out in a row direction are formed in a column direction, characterized in that
a common bus line connecting together respective ones of said opposed voltage signal lines is formed within said display area so that it extends in the column direction.
The liquid crystal display device thus- arranged becomes capable of suppressing any possible distortion of a reference signal being supplied from the common bus line via an opposed voltage signal line toward the opposed electrode because of the fact that the voltage signal line is substantially shortened reducing its electrical resistivity.
And, it is no longer required that any common bus line for common connection of opposed voltage signal lines be provided on the opposite sides of these lines(outside of the display area), which in turn makes it possible to permit shrinkage or down-sizing of a window casing.
In addition, even where an attempt is made to provide a common bus line for use in connecting together the opposed voltage signal lines on their opposite sides (or alternatively on one side), it is still possible to reduce waveform distortion of such reference signal thereby enabling reduction of the line width thereof. Accordingly, window-casing miniaturization may be accomplished.